Apparatus for moving scenery

ABSTRACT

A hydraulic cylinder operating in the tensile mode moves a scenery bar by means of a pulley system. The movement of a cylinder rod of the hydraulic cylinder is conveyed by means of a cable to a drum. The drum turns a lead screw, which moves a travelling nut along a keyway. A pointer attached to the travelling nut indicates the position of the cylinder rod and consequently the height of the scenery bar. Abutment of the travelling nut against a height stop moves a control rod which returns a manual control lever to its off position when a pre-set height is reached. The speed of raising or lowering the scenery bar can also be pre-set.

United States Patent [191 Barnett July- 16, 1974 [54] APPARATUS FORMOVING SCENERY FOREIGN PATENTS OR APPLlCATlONS Inventor: Michael Ian MaxBarnett, Thetford, 268,018 3/1927 Great Britain 254/189 England 1 [73]Assignee: Mole-Richardson (Stage & Studio Primary Examiner-Richard A.Schacher Engineering) Limited, Thetford, Assistant Examiner-Jeffrey V.Nase Norfolk, England Attorney, Agent, or FirmToren, McGeady & Stanger[22] Filed: July 6, 1972 21 Appl. No.: 269,302 [57] ABSTRACT A hydrauliccylinder operating in the tensile mode moves a scenery bar by means of apulley system. The [30] Forelgn Apphcamn. Pfmmy Data movement of acylinder rod of the hydraulic cylinder July 8, Great Brltaln is conveyedmeans of a to a drum turns a lead screw, which moves a travelling nutalong [52] US. Cl 254/141, 254/189, 2 72/22 3 keyway A pointer attachedto the travelling hut [51] Int. Cl B66c 23/60, A63] 1/02 cheat-es theposition of the cyhhdelrod and Cohse [58] Fleld of Search 254/ 141, 189;272/22 quehfly the height Ofthe scenery bah Abutment of the travellingnut against a height stop moves a control References Cited rod whichreturns a manual control lever to its off po- UNITED STATES PATENTSsition when a pre-set height is reached. The speed of 3,404,494 10/ 1968Wolfe 254/189 raising of lowering the Scenery bar can also be P3,690,617 9/1972 Butler.... 6 Cl 6 D F. 3,697,047 10/1972 Cruse 254/141rawmg gums PATENTED JUL 1 61974 SHEET 2 OF 4 NQI PATENTED JUL 1 s 1914SHEET 3 OF 4 w F |G.4.

Q1 .Q/ E s $ikill APPARATUS FOR MOVING SCENERY The invention relates toapparatus for operating stage or television scenery, and moreparticularly relates to hydraulic apparatus for raising or lowering apiece of scenery for instalment in the fly gallery of a theatre. This isa gallery typically about 35 ft. from the floor on the stage and ishidden from the view of the audience. Apparatus for raising or loweringscenery bars to which are attached various pieces of scenery areconventionally operated by men in these fly galleries, using, forexample, systems of pulleys and counterweights.

A conventional method of raising or lowering scenery is to loadcounterweights on to one end of the pulley system, balancing a scenerybar carrying an item of scenery at another end of the pulley system.This process of adding and removing weights in a small gallery above thestage'is a difficult, slow and dangerous process.

Hydraulic mechanisms for moving scenery are also known comprising ahydraulic ram and a pulley system for moving a scenery bar carrying apiece of scenery. A known mechanism comprises a hydraulic ram having avertically acting cylinder rod operating a pulley system, pulley sheavesbeing arranged above and below the ram. This means that a compressiveload is applied to the rod, which must consequently be of substantialconstruction, with the concommitant disadvantages of extra weight andcost. It will be appreciated that cost is an important factor in thisfield, as it may be necessary to have provision for raising and loweringas many as 70 different items of scenery in a single theatre.

Another known mechanism comprises a doubleacting hydraulic cylinder. Apiston is moved hydraulically within the cylinder, and motion istransmitted from the piston to the pulley system by means of asteel-cored nylon cable.

It is desirable to be able to control the speed at which an item ofscenery is moved and the height at which it is to come to rest. This canbe done manually, but this involves a large number of skilled operators.Another possibility is to control the movement of the sceneryelectronically from a central consol. However, in this case, thecontrolbecomes overcentralised. Operators must still be provided in the flygallery to prevent such problems as different items of scenery becomingtangled with or interfering with each other (this is conventionally doneby means of long poles), but these operators are completely divorcedfrom the central control system. Another difficulty is the cost of theelectronic system. If, in order to overcome the disadvantage justreferred to, i.e. overcentralisation of control, individual electronicsystems are provided for the operators in each fly gallery, then thecost becomes prohibitive. Moreover, it has been found that the use ofelectronic systems requires considerable training.

In a preferred embodiment of the invention, a hydraulic cylinderoperating in the tensile mode is arranged on a fly gallery and isconnected to a pulley system to raise or lower an item of scenerymovement of a cylinder rod of the said hydraulic cylinder being conveyedby means of a cable to a drum which rotates a lead screw, the lead screwbeing provided with a travelling nut which is made to move along thelead screw when the lead screw rotates; rotation of the nut beingprevented by a keyway, the nut being provided with a pointer movingalong a scale to indicate the height of the item of scenery; supply ofpressure fluid to the hydraulic cylinder being controlled bya manuallyoperable control lever which is releasably connected to a control rod,the control rod being provided with presettable height stops, wherebywhen the travelling nut abuts one of the stops, the scenery item havingreached a predetermined height, the nut moves the stop and consequentlythe control rod, thereby returning the control lever to its offposition; means being provided for varying the position on the controlrod 'at which the control lever is linked thereto, whereby the Controllever can be pre-set at a given speed of the scenery item.

An advantage of the present invention is that, since the hydrauliccylinder is operating in the tensile mode, the cylinder and cylinder rodcan be made much lighter than would be otherwise possible, i.e., if theywere subjected to compressive loads. Another advantage is that the wholestructure is more stable, and the means required to hold the cylindercan be of simpler and more economical design. For example, the cylindermay be held by a single pivot attachment point at its lower end,

-it being unnecessary to provide means for restraining rotation aboutthe pivot.

A further advantage is that the pre-settable height stops can be set sothat when a predetermined height is reached by the scenery item thecontrol lever is automatically returned to its off position. It is alsopossible to pre-set the height which the scenery item is to reach andthe speed at which it is to reach the set height. A number of sceneryitems can be pre-set in this way, and then all moved simultaneously inthe pre-set manner by turning on a common hydraulic power supply. Thisis an important advantage when it is remembered that there may be from50 to different scenery items to be operated in a given theatre, and asubstantial proportion of these may need to be operated during a 5minute interval between acts. It is possible, for instance, for thespeeds and heights of the various scenery elements to be set during thecourse of an act without actually moving them while the play orentertainment is in progress. However, during the interval, they can allbe moved at the required rate to the required positions by operating asingle button or switch, (i.e., the hydraulic power supply).

A further advantage of the invention is that if a scenery element isbrought to rest by abutment of the travelling nut against one of theheight stops, it is brought to rest gradually, as the control lever isgradually returned to its off position. This is important in that itprevents sudden strains being applied to the apparatus and scenery.

According to the invention there is provided an apparatus for raising orlowering an item of scenery in a theatre, comprising a verticalhydraulic cylinder having a cylinder rod extending from the upper endthereof, the cylinder rod being operatively connected to a pulley systemarranged above said rod, said pulley system being adapted to raise orlower an item of scenery; said hydraulic cylinder being operated bypressure fluid, supply of said fluid being controlled by a valve havinga manually operable control lever; fluid being supplied to the cylinderwhen the lever is in a first position thereof, no fluid being suppliedwhen the lever is in a second position thereof, and fluid being allowedto drain from the cylinder when the lever is in a third position thereofbeyond said second position; the rate at which fluid is supplied to orallowed to drain from the cylinder when the lever is in any positionintermediate the said first and second positions being dependent on theproximity of said intermediate position to the first or second position;the apparatus further comprising a control rod movable in the axialdirection of said rod; releasable means being provided for operativelyconnecting said control lever to said control rod, whereby when saidlever and said rod are operatively connected, the control rod moves inits axial direction in response to movement of the control lever and thecontrol lever is moved by movement of the control rod; the releasablemeans being adapted to connect the control lever to the rod at a rangeof different positions on the rod, whereby while said control rod isstationary, the lever can be set at a predetermined position to allowpressure fluid to be supplied to or drained from the hydraulic cylinderat a selectable predetermined rate; the apparatus being further providedwith a rotatable drum having a cable wound round it, the cable beingconnected to the cylinder rod, whereby motion of the cylinder rodrotates the drum; a lead screw rotated by rotation of the drum; the leadscrew having a travelling nut moved along the lead screw by rotation ofthe lead screw; presettable height stops settable at selectablepositions on the control rod; the lead screw being arranged parallel tothe control rod, whereby the travelling nut moves along the lead screwuntil it abuts one of said height stops, thereby moving the control rodand returning the lever to its second position, wherein no fluid issupplied to the cylinder, thereby stopping an item of scenery attachedto said pulley system at a selectable predetermined height. I

The invention will be further described with reference to, theaccompanying drawings, which illustrate an embodiment of the invention,which is given by way of example only and not by way of limitation.

In the drawings:

FIG. 1 is a side view of a mechanism constituting an embodiment of theinvention, the hydraulic system not being shown;

FIG. 2 is a diagramatic view of the hydraulic system of the mechanism ofFIG. 1;

FIG. 3 is a plan view, with the cover removed of the control box of themechanism of FIG. 1, with two scrap views of the top of the cover;

FIG. 4 is a section through the control box along the line AA;

FIG. 5 is a section through the control box along the line BB; and

FIG. 6 is a detail showing the bevel gear drive of a rotary pointer onthe control box.

A hydraulic ram 1, having a cylinder rod 2 is mounted vertically on awall 3 just above a fly gallery floor by means of a cylinder mountingbracket 4. The cylinder rod 2 carries at its end a first rope sheave 5and a second rope sheave 6. A sheave mounting bracket 7 attached to thewall 3 near the roof 8 has mounted thereupon a third sheave 9, a fourthsheave and a rope anchor 11. Each of the sheaves 5, 6, 9 and 10 has atleast four peripheral groups which accomodate four ropes 11a, 11b, 11c,and-11d, each of which is secured at one end to the rope anchor 11,passes down to sheave 5, round it, then up to sheave 9, round it, downto sheave 6, round it, up to sheave 10 and there to the respective gridsheave assembly 12a, 12b, 120 or 12d,

and then down to a scenery element, shown as scenery bar 13, to whichtheir other ends are secured. The grid sheave assemblies 12a, 12b, 12cand 12d are rotatably held in grid 14 which is fixed to roof 8 of thetheatre. The pulley system is constituted by sheaves 5, 6, 9 and 10,held by members 2 and 7 respectively together with ropes 11a, 11b, 11cand 11d and grid sheave assemblies 12a, 12b, 12c and 12d held by grid14.

The velocity ratio of the pulley system is 4. This is because the flygallery is ordinarily half way between the floor and the ceiling of thetheatre, and, with this particular type of hydraulic cylinderarrangement only half of the height from the fly gallery to the ceilingis avail able for the stroke of the ram. The scenery bar must, however,be able to move the full height of the theatre. The provision of aplurality of ropes attached to a plurality of points of scenery bar 13enables the bar 13 to be maintained horizontal while being raised orlowered, and also enables it to be easily brought close to the grid 14.

Ram 1 is provided with a space 18 which is hydraulically connected, viaconduit 26 to a check valve 27, which is in turn connected hydraulicallyvia conduits 24 and 25 to a four-way spool type directional valve 28operated by a control linkage 22. Valve 28 is further hydraulicallyconnected to pressure line 33 and return line 19. More than onehydraulic cylinder, with its associated check valve, spool valve andcontrol, may be connected to the pressure line and return line. Controllinkage 22 is in turn linked to a control lever 34 by means of a crank35. Thus when pump 60 is switched on, and the valve member is in itsleft-hand position in FIG. 2, pressure fluid is delivered to space 18 ofhydraulic ram 1, causing cylinder rod 2 to be lowered and scenery bar13, with the scenery normally attached thereto, to be raised by acorresponding but magnified amount. In this case the control lever 34 isin its extreme lower position X in FIG. 5.

In FIG. 2, 101 is a tank, 102 is a filter, 103 is a pressure reliefvalve, 104 is an acoustic filter, 105 is a check valve, 106 is a fluidaccumulator, 107 is a pilot operated unloading valve, 108 is a solenoidoperated shut off valve. The function of these members 101 to 108 willnot be described in detail, since these are known components connectedin a conventional manner to provide a pressure fluid supply to pressureline 33 and a return via return line 19. These components form a powerpack which is remotely located in a machinery room.

When lever 34 is in its position Z, the valve member is in its extremeright-hand position and fluid is allowed to drain from space 18 and thescenery bar 13 is lowered. The pressure supplied via conduit 25 to checkvalve 27 acts to open the valve to allow pressure fluid to drain fromspace 18. The rate at which fluid is sup- I plied to or allowed to drainfrom the space 18 is determined by the proximity of lever 34 to itsextreme end positions X and Z. The weight of scenery bar 13 issufficient to force fluid from space 18, so that lowering takes placeunder gravity. In the intermediate position Y of the lever, no fluid issupplied to or drained from the space 18 and bar 13 remains stationary.

Control box 32 comprises a cylindrical drum 35 on which a cable 29 iswound. Cable 29 is secured at one end thereof to a tensioning spring 30and passes round to small sheaves 31 until it reaches the drum,whereafter it returns, by means of sheaves 31 and is secured at itsother end to member 36 which is fixed to rod 2 and to the other end ofspring 30. Thus motion of rod 2 is transmitted by cable 29 and rotatesdrum 35.

Drum is rigidly connected to lead screw 37 so that rotation of drum 35rotates screw 37. Nut 38 is prevented from rotating by keyway 39engaging slot 40 of the nut and is therefore driven up or down the leadscrew when the drum is rotated by movement of the cylinder rod. Thearrangement is such that the nut moves up when the scenery bar is movedup and down when the scenery is moved down. A pointer 41 attached to thenut indicates the position of the nut and consequently the height of thescenery bar with the aid of a linear scale 42 on the cover of thecontrol box. A

rotary pointer 43 is driven by a bevel gear 44 at the end of the leadscrew and moves on a circular scale 45 on the cover of the control boxto provide a'finer indication of the height of the scenery bar. In thisexample, the linear scale is calibrated-in feet and the circular scalein inches, the gear ratio of the bevel gear being such that movement ofthe scenery through 12 inches rotates the rotary pointer once.

The control lever 34 passes through a collar 46 fixed to a control rod47 by means of a screw 51 at an adjustable position. In other words, thecollar can be moved upor down the control rod and secured in a desiredposition. Thus motion of the control lever moves the control rod andvice'verse. The control rod is movable in the direction of its axis, butis prevented from rotating by a key 48. A spring centering device 49 isprovided at the end of the control rod remote from the control lever,the spring of the spring centering device being stronger than the springof the hydraulic valve. As already explained, the degree of opening ofthe hydraulic valve, and consequently the speed at which the scenery barmoves, is controlled by the position of the control lever. The controllever moves over the quadrant scale 50 which is graduated to indicatethe speed of the scenery bar.

The control rod is provided with upper and lower presettable heightstops 53 and 54 respectively, each comprising an adjustable screw 55 or56 respectively running in a slot 52 of the control rod and alsocomprising a sliding block 57 or 58 respectively.

The control box is operated as follows.

If all three adjusting screws are loose the control lever can beoperated manually in the normal way. During a rehearsal, the scenery baris lowered or raised to the required position.

The required height can then be pre-set by means of one of the heightstops, while the speed at which the item of scenery is to move ispre-set by securing the collar to the control rod. The actual speed canbe read from the quadrant scale. It will be noted that this manner ofpre-setting the height and speed requires no special training, since theoperator will already have the feel of the control lever by manualoperation. Upper and lower height stops are provided so that an item ofs scenery can be moved from a pre-set starting height to a pre-set finalheight.

What I claim is:

1. Apparatus for raising or lowering an item of scenery in a theatre,comprising a hydraulic cylinder operatively connected to a pulleysystem, said pulley system being adapted to raise or lower an item ofscenery; said hydraulic cylinder being operated by pressure fluid,supply of said fluid being controlled by a valve having a manuallyoperable control lever; fluid being supplied to the cylinder when thelever is in a first position thereof, no fluid being supplied when thelever is in a second position thereof, and fluid being allowed to drainfrom the cylinder when the lever is in a third position thereof beyondsaid second position; the rate at which fluid is supplied to or allowedto drain from the cylinder when the lever is in any positionintermediate the said first and second positions being dependent on theproximity of said intermediate position to the first or second position;the apparatus further comprising a control rod movable in the axialdirection of said rod; releasable means being provided foroperatively'connecting said control lever to said control rod, wherebywhen said lever and said rod are operatively connected, the control rodmoves in its axial direction in response to movement of the controllever and the control lever is moved by movement of the control rod; thereleasable means being adapted to connect the control lever to the rodat a range of different positions on the rod, whereby, while saidcontrol rod is stationary, the lever can be set at a predeterminedposition to allow pressure fluid to be supplied to or drained from thehydraulic cylinder at a selectable predetermined rate; the apparatusbeing further provided with a rotatable drum having a cable wound roundit, the cable being connected to the pulley system, whereby motion ofthe pulley system rotates the drum; a lead screw rotated by rotation ofthe drums; the lead screw having a travelling nut moved along the leadscrew by rotation of the lead screw; presettable height stops settableat selectable positions on the control rod the lead screw being arrangedparallel to the control rod, whereby the travelling nut moves along thelead screw until it abuts one of said height stops, thereby moving thecontrol rod and returning the lever to its second position, wherein nofluid is supplied to the cylinder, thereby stopping an item of sceneryattached to said pulley system at a selectable predetermined height.

2. Apparatus for raising or lowering an item of scenery in a theatre,comprising a vertical hydraulic cylinder having a cylinder rod extendingfrom the upper end thereof, the cylinder rod being operatively connectedto a pulley system arranged above said rod, said pulley system beingadapted to raise or lower an item of scenery; said hydraulic cylinderbeing operated by pressure fluid, supply of said fluid being controlledby a valve having a manually operable control lever; fluid beingsupplied to the cylinder when the lever is in a first position thereof,no fluid being supplied when the lever is in a second position thereof,and fluid being allowed to drain from the cylinder when the lever is ina third position thereof beyondsaid second position; the rate at whichfluid is supplied to or allowed to drain from the cylinder when thelever is in any position intermediate the said first and secondpositions being dependent on the proximity of said intermediate positionto the first or second position; the apparatus further comprising acontrol rod movable in the axial direction of said rod; releasable meansbeing provided for operatively connecting said control lever to saidcontrol rod, whereby when said lever and said rod are operativelyconnected, the control rod moves in its axial direction in response tomovement of the control lever and the control lever is moved by movementof the control rod; the releasable means being adapted to connect thecontrol lever to the rod at a range of different positions on the rod,whereby, while said control rod is stationary, the lever can be set at apredetermined position to allow pressure fluid to be supplied to ordrained from'the hydraulic cylinder at a selectable predetermined rate;the apparatus being further provided with a rotatable drum having acable wound round it, the cable being connected to the cylinder rod,whereby motion of the cylinder rod rotates the drum; a lead screwrotated by rotation of the drum; the lead screw having a travelling nutmoved along the lead screw by rotation of the lead screw; presettableheight stops settable at selectable positions on the control rod; thelead screw being arranged parallel to the control rod, whereby thetravelling nut moves along the lead screw until it abuts one of saidheight stops, thereby moving the control rod and returning the lever toits second position, wherein no fluid is supplied to the cylinder,thereby stopping an item of scenery attached to said pulley system at aselectable predetermined height.

3. Apparatus as claimed in claim 2, wherein the control rod is providedwith a spring centering device, and the pressure fluid supply valve isprovided with a centering spring, the spring of the spring centeringdevice of the control rod being stronger than the spring of the pressurefluid supply valve.

4. Apparatus as claimed in claim 2, wherein the travelling nut isprovided with a pointer to indicate the height reached by the sceneryelement.

5. Apparatus as claimed in claim 2, wherein the end of the lead screwdrives a rotary pointer to indicate subdivisions of height attained bythe scenery element.

6. Apparatus as claimed in claim 2 wherein said vertical hydrauliccylinder is mounted in a fly gallery of the theatre and includes apiston defining upper and lower spaces in said hydraulic cylinder, andwherein said pulley system has a velocity ratio of 4, with fluid beingsupplied to said upper space of said cylinder when the manually operablecontrol lever of said valve is in said first position, no fluid beingsupplied when said lever is in said second position, and fluid beingallowed to drain from said upper space of said cylinder when the leveris in a third position beyond said second position, with the rate atwhich fluid is supplied to or allowed to drain from said cylinder whenthe lever is in any position intermediate said first and secondpositions being dependent on the proximity of said intermediate positionto the first or second position.

1. Apparatus for raising or lowering an item of scenery in a theatre,comprising a hydraulic cylinder operatively connected to a pulleysystem, said pulley system being adapted to raise or lower an item ofscenery; said hydraulic cylinder being operated by pressure fluid,supply of said fluid being controlled by a valve having a manuallyoperable control lever; fluid being supplied to the cylinder when thelever is in a first position thereof, no fluid being supplied when thelever is in a second position thereof, and fluid being allowed to drainfrom the cylinder when the lever is in a third position thereof beyondsaid second position; the rate at which fluid is supplied to or allowedto drain from the cylinder when the lever is in any positionintermediate the said first and second positions being dependent on theproximity of said intermediate position to the first or second position;the apparatus further comprising a control rod movable in the axialdirection of said rod; releasable means being provided for operativelyconnecting said control lever to said control rod, whereby when saidlever and said rod are operatively connected, the control rod moves inits axial direction in response to movement of the control lever and thecontrol lever is moved by movement of the control rod; the releasablemeans being adapted to connect the control lever to the rod at a rangeof different positions on the rod, whereby, while said control rod isstationary, the lever can be set at a predetermined position to allowpressure fluid to be supplied to or drained from the hydraulic cylinderat a selectable predeTermined rate; the apparatus being further providedwith a rotatable drum having a cable wound round it, the cable beingconnected to the pulley system, whereby motion of the pulley systemrotates the drum; a lead screw rotated by rotation of the drums; thelead screw having a travelling nut moved along the lead screw byrotation of the lead screw; pre-settable height stops settable atselectable positions on the control rod the lead screw being arrangedparallel to the control rod, whereby the travelling nut moves along thelead screw until it abuts one of said height stops, thereby moving thecontrol rod and returning the lever to its second position, wherein nofluid is supplied to the cylinder, thereby stopping an item of sceneryattached to said pulley system at a selectable predetermined height. 2.Apparatus for raising or lowering an item of scenery in a theatre,comprising a vertical hydraulic cylinder having a cylinder rod extendingfrom the upper end thereof, the cylinder rod being operatively connectedto a pulley system arranged above said rod, said pulley system beingadapted to raise or lower an item of scenery; said hydraulic cylinderbeing operated by pressure fluid, supply of said fluid being controlledby a valve having a manually operable control lever; fluid beingsupplied to the cylinder when the lever is in a first position thereof,no fluid being supplied when the lever is in a second position thereof,and fluid being allowed to drain from the cylinder when the lever is ina third position thereof beyond said second position; the rate at whichfluid is supplied to or allowed to drain from the cylinder when thelever is in any position intermediate the said first and secondpositions being dependent on the proximity of said intermediate positionto the first or second position; the apparatus further comprising acontrol rod movable in the axial direction of said rod; releasable meansbeing provided for operatively connecting said control lever to saidcontrol rod, whereby when said lever and said rod are operativelyconnected, the control rod moves in its axial direction in response tomovement of the control lever and the control lever is moved by movementof the control rod; the releasable means being adapted to connect thecontrol lever to the rod at a range of different positions on the rod,whereby, while said control rod is stationary, the lever can be set at apredetermined position to allow pressure fluid to be supplied to ordrained from the hydraulic cylinder at a selectable predetermined rate;the apparatus being further provided with a rotatable drum having acable wound round it, the cable being connected to the cylinder rod,whereby motion of the cylinder rod rotates the drum; a lead screwrotated by rotation of the drum; the lead screw having a travelling nutmoved along the lead screw by rotation of the lead screw; pre-settableheight stops settable at selectable positions on the control rod; thelead screw being arranged parallel to the control rod, whereby thetravelling nut moves along the lead screw until it abuts one of saidheight stops, thereby moving the control rod and returning the lever toits second position, wherein no fluid is supplied to the cylinder,thereby stopping an item of scenery attached to said pulley system at aselectable predetermined height.
 3. Apparatus as claimed in claim 2,wherein the control rod is provided with a spring centering device, andthe pressure fluid supply valve is provided with a centering spring, thespring of the spring centering device of the control rod being strongerthan the spring of the pressure fluid supply valve.
 4. Apparatus asclaimed in claim 2, wherein the travelling nut is provided with apointer to indicate the height reached by the scenery element. 5.Apparatus as claimed in claim 2, wherein the end of the lead screwdrives a rotary pointer to indicate subdivisions of height attained bythe scenery element.
 6. Apparatus as claimed in claim 2 wherein saidvertical hydrAulic cylinder is mounted in a fly gallery of the theatreand includes a piston defining upper and lower spaces in said hydrauliccylinder, and wherein said pulley system has a velocity ratio of 4, withfluid being supplied to said upper space of said cylinder when themanually operable control lever of said valve is in said first position,no fluid being supplied when said lever is in said second position, andfluid being allowed to drain from said upper space of said cylinder whenthe lever is in a third position beyond said second position, with therate at which fluid is supplied to or allowed to drain from saidcylinder when the lever is in any position intermediate said first andsecond positions being dependent on the proximity of said intermediateposition to the first or second position.